Exercise aid



FIG. 1 is a top perspective view of the exercise aid of the design;

FIG. 2 is a right side elevation view;

FIG. 3 is a front end view;

FIG. 4 is a top plan view;

FIG. 5 is a left side elevation view;

FIG. 6 is a back end view; and,

FIG. 7 is a bottom plan view.

The ornamental design for an exercise aid, as shown and described.